Control system calibration

ABSTRACT

A microprocessor-based control system includes an automatic calibration and configuration feature. A calibration and configuration algorithm operates to establish the sensor ranges of all sensors installed and disables certain configurable features if the associated sensors are not present. The algorithm also provides a functional test of the control system during the calibration process.

This application is a division of application Ser. No. 294,537, filedJan. 6, 1989 now U.S. Pat. No. 4,931,967.

This application includes a microfiche appendix including 2 microficheand 140 frames.

A portion of the disclosure of this patent document contains materialwhich is subject to a claim of copyright protection. The copyright ownerhas no objection to the facsimile reproduction by anyone of the patentdocument or the patent disclosure as it appears in the Patent andTrademark Office patent file or records, but otherwise reserves allother rights whatsoever.

This invention relates to a method or system for calibrating an"on-vehicle" control system, such as a hitch control system, forcontrolling the working depth of a tractor-coupled implement as afunction of various sensed and operator-controlled parameters.

Vehicle related electronic control systems typically allow moreflexability in their configuration than do the mechanical controlsystems they replace. This requires some means to define the systemconfiguration of the vehicle. In addition, electronic sensing devicesneed to be calibrated so that each sensing device has a voltage rangewhich is known so that the relation between input voltage and the actualparameter value can be determined. Most electronic systems accomplishthe system configuration by use of DIP switches which must be setmanually when the control system is installed. The input voltage rangeis established by defining a "typical" value and then adjusting theinput sensor manually to ensure that the sensor output matches thepredefined input range.

A second method of calibration and configuration of an onvehicleelectronic system is to plug into a special calibration computer whichcan "down load" calibration and configuration data to the controller.Although this second solution works well at the place of originalmanufacture, it requires expensive special equipment at any repaircenter.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an electronic hitchcontrol system with automatic calibration and configurationcapabilities.

Another object of the present invention is to provide such a calibrationcapability which does not require extra equipment or manual sensoradjustment.

These and other objects are achieved by the present invention whichincludes a microprocessor which executes a hitch control algorithm and acalibration and configuration algorithm.

The calibration and configuration algorithm operates to establish thesensor ranges of all sensors installed and disables certain configurablefeatures if the associated sensors are not present. The algorithm alsoprovides a functional test of the control system during the calibrationprocess. No special equipment, which is not already a part of thecontrol system, is required.

During calibration, a step by step procedure is followed which causesthe control system to operate the hydraulic valves so that the hitch canbe raised and lowered through its full range. Additional steps cause thecontrol system to open the hydraulic valves and slowly close them toestablish the valve preload (dead band) for both the pressure and returnvalves.

The rockshaft control lever is set to a position which defines therockshaft cylinder volume of the tractor and therefore the valve gainsand limits. A secondary control (load/depth mix) is then used toestablish the draft sensor gain. When this procedure is completed,normalization equations are then determined from the range of movementof the input sensors and stored in EEPROM. At end of calibration, thesystem also stores the established valve gains and disables any sensorswhich were not connected to the system during calibration.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified schematic of an agricultural tractor equippedwith the present invention.

FIG. 2 is an electrical and hydraulic schematic diagram of the presentinvention.

DETAILED DESCRIPTION

A tractor 10 includes a rear housing 20 which supports a rear axle 22and rockshaft 24. An implement hitch 26, such as a conventional 3-pointhitch, includes draft links 28 which are connected to lift arms 30 vialift links 32. The lift arms 30 are connected to the rockshaft 24 toensure simultaneous and equal movement, and are raised and lowered via apair of parallel connected hydraulic lift or rockshaft cylinders 34. Adrawbar 36 extends rearwardly from the housing 20. The tractor 10 andthe hitch 26 are merely exemplary and those skilled in the art willunderstand that the invention can be applied to tractors and hitches ofother configurations and to other control systems, such as enginecontrol systems. For example, this invention can be used on anarticulated four-wheel drive tractor or on a front-wheel drive row-croptractor.

An integral-type, ground-engaging implement, (not shown), such as amoldboard plow or a chisel plow, may be attached in a conventionalmanner to the draft links 28. Alternatively, a towed implement (notshown) may be coupled to the drawbar 36. A draft sensor 38 may beinterposed in a strap (not shown) which replaces the hydraulic draftforce sensing cylinder of the conventional production hydromechanicalhitch system to sense the draft force transmitted to the draft links 28from the integral implement. The draft sensor could also be placed inany draft link or a link connected thereto. In the case of a towedimplement, the draft force may be sensed with a draft sensor interposedin the drawbar 36, or with a T-bar coupled to the draft links. In eithercase, any suitable known draft sensor would suffice, such as the ModelGZ-10 manufactured by Revere Corporation of America.

The communication of hydraulic fluid to and from the cylinder 34 or toand from a remote cylinder (not shown) on a towed or semi-integralimplement is controlled by a pair of solenoid-operated electrohydraulicflow control valves 42a and 42b which receive electrical control signalsgenerated by a control unit 50. The flow control valves 42 may be suchas described in U.S. patent appln. Ser. No. 145,345, filed Jan. 19,1988, which is incorporated by reference herein, or a commerciallyavailable alternative.

An operator-controlled command lever 52 is coupled to a lever transducer54 (such as a potentiometer) which generates a command signal whichrepresents a desired hitch position or a desired draft load, or acombination thereof, depending upon the setting of a load/depth or mixcontrol potentiometer 56. An electrical upper position limit signal isprovided by an operator-adjustable potentiometer 51. Also provided is anoperator-adjustable drop rate potentiometer 58.

A position transducer 60, such as a conventional rotary potentiometer,generates a sensed position signal which represents the actual sensedposition of the rockshaft. A position feedback signal could also beobtained from the lift cylinder 34 or from a remote lift cylinder ifthat cylinder includes a position transducer, such as described in U.S.Pat. No. 3,726,191, for example.

Also, a double pole, double throw raise/lower switch 70 may be mountedoutside of the tractor cab near the hitch 26 so that an operator canraise and lower the hitch from outside of the tractor cab. A calibrationswitch 72 is mounted in the tractor cab.

Referring now to FIG. 2, the control unit 50 includes ananalog-to-digital converter 502, a latch 504, an electrically erasable,programmable read only memory EEPROM 506, a microprocessor 508 with anintegral timer (not shown), a display device 510 and a pair of valvedrivers 512. The valve drivers could be any conventional pulse-widthmodulated valve current driver, or other commercially available typesolenoid valve driver, but is preferably of the type described inco-pending U.S. appln. Ser. No. 294,527, filed Jan. 11, 1989, (file13559), now Pat. No. 4,964,014, which is incorporated by referenceherein. The analog signals from sensor/potentiometers 38, 51, 54, 56, 58and 60 are coupled to the microprocessor 508 via analog-to-digitalconverter 502. Latch 504 couples raise/lower switch 70 and calibrationswitch 72 to microprocessor 508. EEPROM 506 stores calibration data usedin a calibration method which is the subject of this invention.

The control unit 50 executes a hitch control algorithm such as isdescribed in detail in co-pending U.S. patent appln. Ser. No. 294,522,filed Jan. 11, 1989 (file 13035), now Pat. No. 4,979,092, which isincorporated by reference herein. The control unit 50 also executes acalibration and configuration computer program which is included in thecomputer program listing contained in the microfiche appendix hereto.The following is a description of the calibration and configurationtechnique which comprises the present invention.

The calibration and configuration software provides a draft sensingconfiguration option wherein the hitch control system can be configuredwith one, two or no draft sensors 38. If no draft sensors 38 areselected, the system will not provide a load sensing option. The draftsensor gain can be selected by the technician during calibration. Theno-load draft sensor zero is read and recorded during the calibrationprocedure. If two draft sensors are available, the hitch control systemwill use the average of these two sensors as its draft load. The systemalso includes a rear raise/lower switch option wherein the rearraise/lower switch 70 option can be detected by the calibration program.If no switch 70 is present, this option will be removed.

In a rockshaft cylinder volume selection configuration option, the valveparameters which control rate of flow and rate of change of flow can beadjusted during calibration so that the hitch can be "sized" fordifferent volumes of the rockshaft cylinder (not shown). In addition,some customization of flow rates can be done to match the hitch tospecial needs.

In a valve preload measurement configuration option, the calibrationdetermines the current required to overcome the preload of the controlvalve 42a, 42b. This value is "saved" and used to provide an adder toall valve commands during normal operation. This provides a means ofreducing the system hysteresis caused by the control valves.

In an automatic sensor spanning calibration function, the range ofoutput voltage from each of the sensors 51, 54, 56, 58 and 60 connectedto the hitch control system are automatically determined when thecalibration procedure is executed. This provides a self-adjustmentmethod which provides freedom from the requirement to do mechanicaladjustments of the sensor linkage. It also provides the flexability touse different sensor ranges for different tractor models.

Because the calibration procedure requires the operation of all controlsystem elements, the control system is functionally tested during thecalibration procedure.

The calibration procedure is a special mode of operation which isactivated by the calibration selector switch 72. This switch can belocated anywhere on the tractor, but is preferably located in thetractor cab. Once calibration mode is selected, a technician canconfigure the hitch control system by following a special calibrationprocedure. At the end of calibration, the calibration switch 72 must beturned to normal mode which will cause the calibration program to recordthe calibration data into the non-volatile memory 506 (EEPROM). Thesecalibration data will include slope and intercept type information forall input sensors, as well as rockshaft cylinder volume adjusted valveparameters.

A calibration timer (not shown) is also incorporated so that switchbounce and wiring harness faults will not cause loss of calibrations.This feature can be used to recall previous calibrations to determinecause of hitch system malfunctions.

The hitch calibration program is called by a main control loop when thecalibration input switch 72 is turned to calibration mode. When thecalibration mode switch is returned to normal mode, the calibrationinformation is stored into the permanent memory 506 (EEPROM). Thiscalibration data is then used by the normal algorithm to normalize theinput data of all sensors. The normalization equation is of the form:

    Y=M×(X-B)

where

Y is the normalized output,

M is the slope determined by the calibration routine,

X is the sensor input read by the analog input device, and

B is the X-intercept (or sensor zero reading) stored by the calibrationroutine.

In addition, the algorithm initialization routine can detectuncalibrated sensors and flag them for the normal algorithm to ignore.Valve parameters set by the calibration routine will provide valve gainsand valve current limit values as well as offsets required to overcomethe valve preloads.

When the calibration switch 72 is in calibration mode, the calibrationprogram will monitor all sensor inputs. These inputs will be compared toa stored minimum and maximum table which is used to provide a minimumand maximum sensor reading on all sensors during the duration of thecalibration. When calibration is complete, these readings are used toestablish a sensor calibration which will be used by the normal controlalgorithm. The value of these minimums and maximums are used todetermine the presence of optional sensors. The minimum and maximums areused differently for draft sensors 38 than for all other sensors.

The average of the minimum and maximum of each draft sensor 38 is usedto establish a draft zero reading. The draft sensor slope is "entered"by the operator by the setting of the mix control 56 at the end ofcalibration. If draft sensor minimum and maximum readings differ by morethan 0.5 volts, the draft sensor 38 will be considered failed. The draftsensor maximum zero reading and the draft sensor slope are used to"project" the sensor reading at 133% of rated draft. If this value wouldexceed 4.69 volts, the draft sensor 38 will be considered failed.Likewise, if the draft sensor minimum zero reading and the draft sensorslope would give a projected reading at -67% of rated draft of less than0.31 volts, the sensor will be considered failed. Since failed sensorswill be disabled by the main algorithm, an "out-of-range" zero readingcan be used to indicate no sensor present. This can be achieved bygrounding the sensor input.

For non-draft sensor inputs, the sensor minimum and maximum are used todevelop a zero and slope for a normalization routine of the mainalgorithm. The difference between the sensor minimum and sensor maximummust be greater than 1.5 volts or the sensor will not be calibrated. Ifsensor minimums are less than 0.31 volts or if sensor maximums aregreater than 4.69 volts, the sensor will be considered failed. If therange of sensor movement is less than 0.5 volts, the sensor will beconsidered uncalibrated and the previous calibration will be retained.If the range of sensor movement is greater than 0.5 volts but less than1.5 volts, the sensor will be considered failed and no calibration datawill be stored. As for draft sensors, failed other types of sensors willbe disabled by the main algorithm, so "out-of-range" zero readings canbe used to define sensor options. This can be achieved by grounding thesensor input.

The rear raise/lower switch 70 has one normally closed and one normallyopen contact for each position (raise or lower). If no switch ispresent, these inputs will be all open. This condition is used as a flagto tell the algorithm that the rear raise/lower switch option is notpresent. The algorithm automatically disables functions associated witha sensor which is not connected to the control unit. For example, onpage 38 of the microfiche computer program listing, the lines beginning"JC DRFT04" cause the program to skip or disable the draft sensor signalaveraging functions if only one draft sensor is connected to the controlunit.

In order to determine the minimum and maximum sensor readings on thecontrol inputs 51, 54, 56, 58, the controls are moved through their fullrange of movement. However, the hitch position sensor 60 can best bemoved through its range of movement by means of the hitch controlsystem. Likewise, the valve preloads can best be determined by applyinga known current and measuring the flow rate of the valves 42a or 42b.This can be accomplished on the tractor by using the hitch controlsystem to apply the current and measuring the flow rate with the hitchposition sensor 60. The adjustment of the custom raise rate can also bedone by adjusting the hitch control system to obtain the desired raiserate and then "locking" it in.

Hitch movement for normal calibration is accomplished by using therockshaft control lever 52 in "open loop" mode. That is, lever positionsin the lower half of the lever slot (not shown) will cause the returnvalve 42b to open and lever positions in the upper half of the slot willcause the pressure valve 42a to open. The command is proportional to thedistance from the center of the slot. Therefore, the valve command isvariable from "off" at the center to "full on" at either end. With thistype of valve control, the hitch 26 can be made to raise and lower in acontrolled manner so that the calibration routine can read the minimumsand maximums from the hitch position pot 60.

Valve preload currents are determined by opening the valve 42a or 42buntil hitch movement is achieved and then closing the valve slowly untilthe movement stops. This preload calibration is activated by theoperator. This can be done when the hitch 26 is at either limit and thelever 52 is at the same limit. Turning the raise limit 51 from end toend will activate the valve preload calibration. The valve beingcalibrated will depend on the hitch (and lever) position. A full uphitch will calibrate the return valve 42b, a full down hitch willcalibrate the pressure valve 42a.

Raise rate (the rate at which the control system will move the hitchupwards) calibration can be adjusted by use of the drop rate control 58.This control allows two options. A normal mode is to move the drop ratecontrol 58 end-to-end after the lever and hitch position pots have beencalibrated and the valve preloads have been determined. This willprovide the "standard" raise rate. A second mode is to move the droprate control 58 as the first pot to be moved. This provides a "raiserate only" calibration mode of operation. When this mode is selected, noother calibrations are determined or stored. Since draft sensor zeroesand hitch position calibrations will not be recorded, this method ofraise rate calibration can be done with an implement installed.

To operate this "raise rate only" mode, the following steps areperformed:

1. Set the rockshaft control lever full forward.

2. Set the hitch into calibration mode. A code will be displayedconfirming that the calibration mode has been selected.

3. Rotate the drop rate pot full counterclockwise, full clockwise andback to mid position. This will set the hitch controller to raise rateadjustment mode and set the raise rate to the standard value. A 235 willbe displayed indicating the standard raise rate has been selected.

4. Move the rockshaft control lever full back and bring it full forwardslowly. If the hitch is not full down, it should go full down at thistime. The display should remain at 235.

5. Move the rockshaft control lever full back. The hitch will go full upat the standard raise rate. To establish a custom raise rate, rotate thedrop rate pot in a clockwise direction to increase the rate, and in acounterclockwise direction to decrease the rate. More clockwise willincrease the raise rate more and more counterclockwise will decrease theraise rate more. When the raise rate is less than the standard, thedisplay will be 234 and when greater than the standard, the display willbe 236. Continue to lower and raise the hitch until the desired raiserate is established. Note that when a heavy implement is used duringthis test, the lever should always be moved forward very slowly toprevent the implement from dropping too rapidly.

6. Return the hitch to normal (not calibrate) mode.

When the drop rate control is used to establish the raise rate, thehitch control lever 52 can be used in open loop mode to observe the rateat which the hitch 26 moves. The setting of the drop rate control 58toward counterclockwise will reduce the raise rate and the settingtoward clockwise will increase the raise rate. The setting of thiscontrol when raise rate evaluation is completed will establish the raiserate (valve current limts) to be stored.

In order to provide flexability of the hitch configuration, twoadditional parameters are established. They are the rockshaft cylindervolume and the draft sensor gain (slope). The rockshaft cylinder volume(and associated valve gain terms) is established by the location of therockshaft control lever 52 either at end of calibration or at the timethe drop rate pot 58 is first calibrated. Note that if the rockshaftcontrol lever 52 is not moved during a calibration, the valve gain termswill not be modified.

The draft sensor gain is only required on draft sensing hitches. Sincethe load/depth control 56 is likewise only required on these hitches,the load/depth control setting at end of calibration will establish thedraft sensor gain value.

In order to achieve the flexability of this calibration procedure, theprogram monitors all sensor inputs and determines the one that was mostrecently moved. This control is then considered active so that the hitchoperation will reflect the output associated with that input. Controlsduring calibration are quite similar to controls during normal operationso that the calibration technician will achieve hitch operation similarto that which would be expected. For example, the only controls that canmove the hitch 26 are the main control lever 52 and the raise limitcontrol 51. The hitch will move down with the lever forward and up withthe lever rearward. A rotation of the raise limit control 51counterclockwise will lower the hitch 26 in calibration as well as innormal operation and likewise, clockwise raises the hitch 26 in bothcases. The movement of any control other than the active control willturn the hitch output off. The hitch lever 52 must be "unlocked" bymoving through zero in order to move the hitch 26.

To operate this calibration and configuration technique, an operatorperforms the following steps:

1. Set the rockshaft control lever full forward.

2. Set the hitch into calibration mode. A code will be displayedconfirming that the calibration mode has been selected.

3. Move the rockshaft control lever full back and full forward. If thehitch is not full down, it should go full down at this time. Either 164or 165 will be displayed.

4. Move the rockshaft control lever full back. The hitch should go fullup at this time. The display will be 100.

5. With the hitch full up, use the raise limit control to determine thereturn valve preload. Rotate the raise limit to the fullcounterclockwise position and back to the full clockwise position. Againmove the control to the full counterclockwise position as you observethe hitch. The hitch should move at least one-fourth down and then stop.If the hitch does not go down, move the raise limit control back to midrange and again to the full counterclockwise position. After the hitchhas moved down and stopped, the display will change from a numbergreater than 100 to a number less than 100. This indicates that thereturn valve preload has been determined.

6. Move the rockshaft control lever full forward and again fullrearward. The hitch will come full up. The display will be 100.

7. With the hitch full up, use the raise limit control to set the returnvalve preload. Rotate the raise limit from the full counterclockwiseposition back to the full clockwise position. This will recall thereturn valve preload recorded in step 5. Move the control to the fullcounterclockwise position and observe the hitch. The hitch will move atleast one-fourth down and then stop. After the hitch has moved down andstopped, the display will change from a number greater than 100 to anumber less than 100. This indicates the preload has been determined.

8. Move the rockshaft control lever full forward. The hitch will go fulldown. The display will be 165.

9. With the hitch full down, use the raise limit control to determinethe pressure valve preload. Rotate the raise limit to the clockwiseposition and back to the full counterclockwise position. Again move thecontrol to the full clockwise position and observe the hitch. The hitchshould move at least one-fourth up and then stop. If the hitch does notmove up, move the raise limit control back to mid range and again to thefull clockwise position. After the hitch has moved up and stopped, thedisplay will change from a number greater than 100 to a number less than100. This indicates that the pressure valve preload has been determined.

10. Move the rockshaft control lever full rearward and again fullforward. The hitch will go full down. The display will be 165.

11. With the hitch full down, use the raise limit control to set thepressure valve preload. Rotate the raise limit from the full clockwiseposition back to the full counterclockwise position. This will recallthe pressure valve preload recorded in step 9. Move the control to thefull clockwise position and observe the hitch. The hitch will move atleast one-fourth up and then stop. After the hitch has moved up andstopped, the display will change from a number greater than 100 to anumber less than 100. This indicates the preload has been determined.

12. Move the rockshaft control lever full back. The hitch will come fullup. Move the rockshaft control lever slowly forward while observing thedisplay. Set the lever to achieve the rockshaft volume index numberwhich is appropriate for the tractor being calibrated. Leave it in thisposition until calibration is completed. The following table sets forththe index codes which are displayed for different numbers of lift assistcylinders.

    ______________________________________                                                       No. of                                                         Tractor        Lift Cyl.                                                                              Display                                               ______________________________________                                        Row-crop       0        127                                                                  1        129                                                                  2        131                                                   4-WD           NA       137                                                   ______________________________________                                    

13. Rotate the drop rate pot to full counterclockwise and back to fullclockwise. A 235 will display, indicating that the drop rate pot hasbeen calibrated.

14. (With draft sensing only): Rotate the load/depth mix control to thefull counterclockwise position, then to the full clockwise position. Thetractor will display 233. This number indicates the position of the mixcontrol. While observing the display, adjust the mix control to displaythe draft sensor span index number of 183.

15. If the above procedure was correctly followed and no errors weredetected during calibration, proceed to Step 17.

16. If problems have occurred in attempting to follow this procedure andyou do not wish to update the hitch controller calibration memory, turnthe tractor keyswitch off before returning the hitch to normal (notcalibrate) mode. This will abort the calibration procedure and restorethe calibration memory to that which was present prior to thisoperation.

17. Return the hitch to normal (not calibrate) mode.

While the invention has been described in conjunction with a specificembodiment, it is to be understood that many alternatives, modificationsand variations will be apparent to those skilled in the art in light ofthe aforegoing description. Accordingly, this invention is intended toembrace all such alternatives, modifications and variations which fallwithin the spirit and scope of the appended claims.

We claim:
 1. In a hitch control system having a rockshaft hydrauliccylinder for moving the hitch under th control of a control valve, acontrol unit for controlling operation of the control valve in responseto movement of an operator-movable command lever and in response to atleast one sensed parameter such as a draft force parameter and a hitchposition parameter, and a display connected to the control unit, thecontrol unit comprising:means for storing control valve parametersassociated with different volumes of rockshaft cylinders; means forstoring index values, each index value being associated with aparticular volume of a rockshaft cylinder and with at least one of thestored control valve parameters; means for selectively displaying acertain one of the stored index values depending upon the position ofthe command lever; and means for selecting said at least one of saidstored control valve parameters which is associated with the displayedindex value, the control unit controlling the control valve as afunction of the sensed parameter, the command lever and the selectedcontrol valve parameters.
 2. The hitch control system of claim 1,further comprising:an operator movable rate limit setting device coupledto the control unit, the control unit controlling operation of therockshaft cylinder so that the hitch moves at a rate corresponding to arate limit value; and the control unit having a calibration mans foradjusting a rate at which the rockshaft cylinder moves the hitch, thecalibration means adjusting the rate limit value in response toadjustment of the setting device when the command lever is operated tomove the hitch away from a limit position.
 3. The hitch control systemof claim 1, further comprising:a sensor for sensing the position of thehitch; and a solenoid operated spring-biased value for controlling fluidflow to and from the rockshaft cylinder, the control unit including mansfor controlling energization of the valve solenoid and determining anamount of solenoid preload current required to overcome the spring biasof the valve, the energization controlling means comprising: means forapplying a certain amount of current to the solenoid sufficient to causethe valve to cause the rockshaft cylinder to move the hitch; and meansfor gradually reducing the current applied to the solenoid until a rateof change of the sensed position of the hitch drops below a certainlevel, whereby the last reduced current is the solenoid preload current.